.alpha.-Ketocarboxylic acids are a valuable class of chemical compounds having utility in chemical synthesis, biochemical processes, and the like. It has recently been discovered that .alpha.-keto analogues of essential .alpha.-amino acids, and salts thereof, are highly effective for the treatment of patients suffering from chronic kidney failure, i.e., uremic poisoning. See, for example, Walser, Clinical Nephrology, Vol. 3, pp. 178-186 (1975) and citations therein. Calcium salts of such .alpha.-ketocarboxylic acids are especially important, since the use of calcium rather than e.g., sodium, as the cation substantially reduces problems of ionic balance, which are particularly critical in the case of kidney disorders.
Accordingly, it would be highly desirable to have available a simple, high yield, economical process that can be readily adapted for large-scale production of calcium salts of such .alpha.-ketocarboxylic acids.
There are a number of methods for preparing calcium salts of carboxylic acids that are well known in the art and that could be initially considered in the instant situation. One method involves the preparation of a water soluble alkali metal salt followed by precipitation of the calcium salt by exchange, for example, by treatment with a solution of a calcium halide. However, such a method does not work in the instant case since the calcium salts of interest with the exception of calcium .alpha.-ketoisocaproate, are substantially water soluble. Another method involves the preparation of a calcium salt from the free acid by treatment with calcium carbonate in water, followed by concentration of the aqueous solution of the calcium salt thus formed. In the case of calcium .alpha.-ketoisovalerate and calcium .alpha.-keto-.beta.-methylvalerate, such method, while operable, is tedious to perform on a large scale.